Larynx: Acute and Chronic Effects of Blunt and Penetrating Trauma
- Computed tomography is the imaging examination of choice for evaluating blunt force and penetrating trauma and complications of all forms of upper airway injury.
- Computed tomography is an ideal complement to clinical and endoscopic examinations.
- Swallowing studies are still sometimes useful.
- Acute injury must be diagnosed and treated within 3 to 7 days for optimal outcome.
- The status of the cricoid cartilage is a critical prognostic element.
- Laryngeal injury is sometimes overlooked in multitrauma victims with more obviously life-threatening problems.
The larynx is commonly injured accidentally or iatrogenically. Iatrogenic trauma is discussed in conjunction with subglottic stenosis (Chapter 208). The treatment principles for the injured larynx have been in place for decades and well before the advent of computed tomography (CT) and magnetic resonance imaging (MRI). Treatment has varied little since this earlier reported experience; however, triage, planning, and prognosis are now executed in a more informed context because of diagnostic imaging input.
The imaging appearance of an injured larynx depends directly on the mechanism of injury. Imaging, almost entirely nowadays with CT, shows the extent of injury to the laryngeal skeleton and related tissues. In the late 1970s and into the 1980s CT, significantly advanced our understanding of how the larynx responds to blunt and other forms of trauma.1–3 Imaging with CT, and occasionally other studies, takes its place alongside endoscopy on the critical path for triage of laryngeal injuries to proper management plans.
A thorough knowledge of the following anatomy and anatomic variations of normal in each of the following areas is required for the evaluation of laryngeal trauma. This anatomy is presented in detail with the introductory material on the larynx, hypopharynx, cervical esophagus, and infrahyoid neck in general:
Evaluation of Primary Laryngeal and Hypopharyngeal Injury
- Larynx, including the laryngeal skeleton, deep tissues spaces within the larynx, mucosal landmarks, and functional structures within the larynx (Chapter 201)
- Hypopharynx (Chapter 215)
- Tongue base region and low oropharyngeal wall (Chapter 190)
- Cervical esophagus, most importantly the esophageal verge junction with the postcricoid portion of the hypopharynx (Chapter 221)
- Trachea (Chapter 209)
Evaluation of Injuries to Extralaryngeal Structures
- Visceral compartment of the neck and related fasciae (Chapter 149)
Evaluation of Related Vocal Cord Dysfunction and Nerve Injury
- Knowledge of the entire course of the vagus and recurrent laryngeal nerves on both sides (Chapter 201)
Techniques and Relevant Aspects
The neck should always be slightly hyperextended for laryngeal CT. This pulls the larynx higher in the neck, thus reducing artifacts produced by the shoulders. This may not be possible if the neck has been immobilized in an acutely injured patient.
Laryngeal images must be viewed as parallel to the TVCs. This angle is usually selected from a preliminary lateral digital image. In acute trauma patients, angling may impede optimal data acquisition for brain or cervical spine studies, so the axial images may be retrospectively reformatted from a volume set of image files or reconstructed from volume raw data files if the acquisition angle of the gantry is not optimized for the laryngeal anatomy by being parallel to the TVCs. Sections made or viewed oblique relative to the TVC can produce substandard images that lead to interpretative difficulties and possibly treatment mistakes. Skewed image review may lead to a wrong interpretation of the anatomic relationships in the transglottic region that are often critical to medical decision making. Slice thickness (SLT) should be no more than 1 to 3 mm in detailed laryngeal studies. If angled axial reformations or reconstructions are anticipated, then section SLT must be kept between 1 and 2 mm. This will also assure good-quality multiplanar reformation. The field of view of the larynx should be as small as possible to optimize spatial resolution. A second reconstruction with a larger field of view should be included for evaluation of regional anatomy that may also be traumatized. Adequacy of the technique used can be measured by whether it produces artifactfree images with excellent fine detail of the paraglottic space at the level of the TVCs and laryngeal skeletal detail.
In general, these requirements are simply fulfilled on multidetector computed tomography (MDCT) $16 slices by obtaining a volume set of data with nominal SLT of 1.0–1.5 mm and then reconstructing the volume to fulfill the criteria just set forth. An example of protocols applied to MDCT $4 detector rows is summarized in Appendix A.
Intravenous contrast is only selectively used in studies of laryngeal trauma. A compelling reason to use contrast occurs infrequently. This is mainly for studies that are done at least a few days after trauma when secondary infection of the laryngeal skeleton or neck infection due to a false passage is suspected. CT angiography may be added if there is evidence of active bleeding or other cause to suspect a vascular injury as well as an injury of the larynx.
Magnetic resonance (MR) studies, if done, should use receiver coils that are custom designed to study the neck. Small loop or posteriorly placed surface coils meant to study the spine are not adequate. The use of intravenous paramagnetic contrast is individualized, but generally it should not be used. Specific protocols are presented in Appendix B.
Pros and Cons
CT is the primary imaging examination for blunt, penetrating, and iatrogenic trauma as well as for retained foreign bodies. CT is a major advantage for the laryngologist in this regard. A patient with severe head and neck injuries presents no problem for safe and convenient laryngeal imaging at the same time the brain, face, and cervical spine and multiple other systems are evaluated by MDCT at initial intake. This is particularly important in multisystem trauma due to motor vehicle accidents since this is the most common cause of blunt laryngeal trauma.
CT may be used to screen for false passages but cannot be used to exclude such mucosal injury. Swallowing studies are used to screen for false passages as suggested by endoscopic evaluation.
MRI is almost never used for the evaluation of acute trauma and is very infrequently indicated in chronic conditions. It has been used very selectively for chronic traumatic conditions resulting in very unusual circumstances where the prevertebral space or neural elements might be involved in the disease process.
There is some debate about whether patients suspected of having false passages should be evaluated with barium or water-soluble contrast. This debate centers on the risk of particulate contrast being deposited in an infected space in the neck versus the risk of the pulmonary toxicity of aspirated water-soluble contrast. In general, even though the contrast is suboptimal for visualization of subtle leaks, water-soluble contrast is used.
Blunt and Penetrating Laryngeal Trauma and Aspirated Foreign Bodies
Blunt laryngotracheal trauma most commonly is due to a force applied from anterior to posterior. The most common impacts are between the neck and a dashboard, a punch of some sort to the neck, or a “clothesline” type of mechanism of injury. The final common pathway in these events is compression of the larynx between the source of the force and cervical spine (Figs. 207.1–207.5). The amount and vector of the applied force, area impacted, and contour of the offending object all contribute to the extent of injury. There are other factors that influence the pattern of injury as well (Figs. 207.1–207.5).
False passages and their complications that might accompany laryngeal blunt force trauma typically affect the hypopharynx rather than the larynx and are also discussed in conjunction with hypopharyngeal injuries (Figs. 207.5C and 207.6).
Penetrating injuries are most frequently related to stab and gunshot wounds. These will usually be evaluated in conjunction with more potential serious injuries to the brachiocephalic vessels in penetrating neck injuries.
Very severe blunt trauma and crush injuries may lead to a combination of findings and considerations seen in both blunt and penetrating mechanisms (Fig. 207.7).
Prevalence and Epidemiology
Blunt laryngeal trauma is a sporadic occurrence that mainly is associated with motor vehicle accidents. Clothesline-type injuries are more associated with motorcycle, all-terrain vehicle, and bicycle accidents. Assaults and fights make up the bulk of other blunt-force trauma to the neck. Blunt and penetrating insults may occur with the same incident. Penetrating injuries are relatively uncommon. Retained foreign bodies are usually in the pharynx rather than the larynx.
Blunt-force and penetrating injuries of the larynx and trachea may compromise critical functions. Airway maintenance is always the primary concern. Once the airway is secured, therapy is focused on preserving other glottic function, including a normal voice and assuring swallowing without aspiration. Acute injuries require a rapid examination that is accurate and free of potential added morbidity.
Clinical evaluation may suggest laryngeal injury; however, this possibility may be overlooked when other extensive head and face injuries are present in the absence of life-threatening airway obstruction. Swelling of the cervical soft tissues can hide gross disruption of the normal laryngeal skeleton from palpation (Fig. 207.3). Failure to acutely establish the extent of laryngeal injury can lead to a laryngeal stenosis that has typically proven more difficult to manage at a later time. Delayed or lack of definitive treatment can lead to a less satisfactory outcome (Figs. 207.8–207.10).
Classification systems for laryngotracheal complex injuries have been suggested for many years. Injury may involve one or more of these sites, but such classification remains a useful structure for discussing the diagnosis and management of blunt trauma. This clinical classification will be used in the following discussion of diagnostic imaging:
- Soft tissue
- Soft tissue
- Chronic stenosis